The photodynamic therapy (PDT), according to which photosensitizers having a specific affinity for tumor cells are administered to patients before irradiation by laser beams of various wavelengths for treatment of cancers, is now attracting attention as a non-invasive therapy for cancers. Known photosensitizers usable for the PDT include various derivative compounds having a porphyrin skeleton, some of which are used clinically.
Desirable photosensitizers usable for PDT are required to be hydrophilic and highly selective to tumor cells and to have a large molar extinction coefficient at a long-wavelength range. Long wavelength light shows a good penetrating property to tissues and allows the use of an inexpensive laser irradiator. However, the porphyrin derivatives proposed so far have problems such as their hydrophobicity that causes side effects and their small molar extinction coefficient for long-wavelength light range. Therefore, the development of superior photosensitizers is desired.
For the purpose of solving these problems, Japanese Unexamined Patent Publication No. 2000-7693 generally discloses hydrophilic tetraphenylchlorin derivatives and bacteriochlorin derivatives with saccharide residues on phenyl groups which have a larger molar extinction coefficient to the long-wavelength light compared to the porphyrin derivatives. However, the publication does not actually disclose the synthesis of the bacteriochlorin derivatives and their effects as photosensitizers.